The present invention relates to a mud saver valve which allows the downward flow of drilling mud but closes when pumping is interrupted to retain mud within the drill string.
U.S. Pat. No. 4,962,819 (Bailey et al 1990) describes the utility of inserting into a drill string, between a kelly and drill pipe, a mudsaver valve. Such a mudsaver valve saves in mud costs, reduces pollution and provides a safer working environment for rig workers. With prior art mudsaver valves a closure plug at a lower end of the mudsaver valve would tend to leak after becoming eroded and worn. The closure plug could not be repaired and eventually had to be replaced. The Bailey et al reference taught how to make the mudsaver valve repairable through the use of an inner sleeve supported within an upper end of the mudsaver valve by retaining bolts. The inner sleeve served to house the closure plug. The use of retaining bolts enabled the inner sleeve to be retrieved for servicing when the closure plug was worn to the point that unacceptable leakage was occurring. More importantly, it enabled the inner sleeve to be retrieved when immediate access was required when problems were encountered during drilling.
The present invention relates to an alternative configuration of mudsaver valve with retrievable inner sleeve.
According to the present invention there is provided a mudsaver valve with retrievable inner sleeve which includes a housing having an axis and a inner sidewall defining an interior bore. An inner sleeve is disposed within the interior bore of the housing. The inner sleeve has a first end, a second end, a central passage extending between the first end and the second end, at least one inlet passage into the central passage at the first end and at least one radial outlet passage from the central passage at the second end. An annular flow control sleeve is positioned between the inner sidewall of the housing and the second end of the inner sleeve. An annular piston is positioned between the inner sidewall of the housing and the first end of the inner sleeve. The annular piston is axially movable relative to the housing. The annular piston is secured to the first end of the inner sleeve such that movement of the annular piston results in movement of the inner sleeve relative to the annular flow control sleeve between a valve closed position and a valve open position. In the valve closed position the at least one radial outlet passage of the inner sleeve is blocked by the annular flow control sleeve. In the valve open position the inner sleeve is moved relative to the annular flow control sleeve so that the at least one radial outlet passage is no longer blocked. A biasing spring biases the annular piston to maintain the inner sleeve in the valve closed position. The inner sleeve is maintained in the valve closed position until pump pressure acting upon the inner sleeve and the annular piston overcomes the biasing force of the biasing spring causing the inner sleeve and annular piston to move to the valve open position. When pump pressure ceases, the biasing spring acts upon the annular piston which carries the inner sleeve back to the valve closed position.
The mudsaver valve, as described above, provides an alternative valve configuration which has some inherent advantages over the Bailey et al reference. The inner sleeve moves between the valve open position and the valve closed position. A positive seal is maintained even as erosion and wear occurs. In contrast, the configuration of mudsaver valve disclosed in the Bailey et al reference inevitably leaked as soon as erosion and wear began to occur.
Although the mudsaver valve disclosed in the Bailey et al reference was serviceable, the process of retrieving the retrievable sleeve would shear the retaining bolts. This made it impossible to immediately inspect and reinsert the retrievable sleeve. In contrast, with the present mudsaver valve the annular piston is detachably secured to the first end of the inner sleeve by means of a spring retaining ring. This enables inner sleeve to be removed merely by overcoming the biasing force of the spring retaining ring and then snapped back into place after inspection. It is, of course, preferred that a coupling be positioned at the first end of the inner sleeve, whereby the inner sleeve is grasped for removal.
With the mudsaver valve disclosed in the Bailey et al reference the biasing spring used was exposed to corrosive drilling fluids. With the present invention it is preferred that a lubrication port extend through the inner sidewall of the housing. This permits lubrication of the biasing spring. As long as the biasing spring remains immersed in lubricant, it is protected from the effects of corrosive drilling fluids and hydrogen sulfide gas.
Although beneficial results may be obtained through the use of the mudsaver valve, as described above, pressure differentials sometimes develop which can adversely affect the operation of the mudsaver valve. Even more beneficial results may, therefore, be obtained when a one way valve is positioned at the second end of the inner sleeve. The one way valve prevents a flow of fluids from the first end to the second end, but permits a flow of fluids from the second end to the first end should a pressure differential occur.
The configuration of mudsaver valve, as will hereinafter be further described, can be fortified against erosion through the use of carbide. It is preferred that the inlet passages be lined with carbide bushings and the radial outlet passages be lined with carbide bushings. It is also preferred that the annular flow control sleeve have a carbide bushing aligned with radial outlet passages when the inner sleeve is in the valve open position.